The present invention relates generally to an electric device, including, but not limited to, an electric motor, a generator, or a regenerative motor (collectively referred to herein as “electric devices”, “electro-magnetic devices”, “electric machines”, etc.). The term regenerative motor is used herein to refer to a device that may be operated as either an electric motor or a generator. The electric device could be one or more components in a composite device. An example of such a composite device is a compressor comprising one or more electric motors, where the one or more electric motors may be integral with a fan. Preferably, the present invention relates to a highly efficient electric device having improved characteristics. More preferably, the present invention relates to a highly efficient electric device capable of operating at high frequencies.
High Frequency Electric Devices
The electric motor and generator industry is continuously searching for ways to provide motors and generators with increased efficiencies and power densities. The power of an electro-magnetic device is related to the frequency of the device, such that an increase in the frequency of the device increases the power. Thus, machines with higher frequencies are often desired when increased power is desired. The synchronous frequency of a synchronous electric machine can be generally expressed as f=S·P/2, where f is the frequency of the machine in Hz, S is the speed in revolutions per second, and P is the pole count of the machine. From this, it is seen that as the speed of the machine increases, the frequency increases, and the power increases. Likewise, as the pole count increases, the frequency of the machine increases, and the power of the machine increases. However, it is significant to note that as the pole count increases, the changes in the magnetic field for the machine also increase, and additional heat is generated within the machine, thereby contributing to the inefficiency of the machine.
Past attempts to manufacture high frequency electric machines (i.e., electric machines with a frequency greater than 300 Hz) typically involved low pole counts at high speeds, since lower pole counts generally help to reduce the core losses, while higher pole counts generally increase the core losses. However, the significant core losses seen with conventional higher pole machines is mainly due to the fact that the material used in the vast majority of old machines is a conventional silicon-iron alloy (Si—Fe), which contains about 3½% or less by weight of silicon. In particular, losses resulting from the changing magnetic fields at frequencies greater than about 300 Hz in conventional Si—Fe-based materials causes the material to heat to the point where the device cannot be cooled by any acceptable means. Accordingly, a commercially viable high frequency electric machine has been difficult to achieve, and therefore it would be desirable to produce a commercially viable high frequency electric machine. It would also be desirable to provide an electric device that can operate simultaneously at a high frequency with a high pole count resulting in a cost-effective electric device having low magnetic core loss and high power density.
Amorphous Metal Magnetic Cores
The advent and subsequent study of amorphous metals has caused many to believe that motors and generators made with amorphous metal magnetic cores have the potential to provide substantially higher efficiencies and power densities compared to conventional motors and generators. In particular, amorphous metals exhibit promising low-loss characteristics, leading many to believe that a stator made with a magnetic core of amorphous metal would result in an electric machine with increased efficiencies. However, previous attempts at incorporating amorphous material into conventional machines failed since these attempts simply involved substituting amorphous material for the silicon-iron in conventional magnetic cores of lower frequency electric machines. This resulted in electric machines having increased efficiencies with less loss, but with a subsequent loss in power output and significant increases in cost associated with handling and forming the amorphous material.
For example, U.S. Pat. No. 4,578,610 discloses a highly efficient motor having a stator constructed by simply coiling a strip of amorphous metal tape, wherein the amorphous strip is wound and then slotted and a suitable stator winding is then placed within the slots.
U.S. Pat. No. 4,187,441 discloses a high power-density machine having spirally wound laminated magnetic cores made from amorphous metal ribbon having slots for receiving stator windings. The patent further discloses using a laser beam for cutting the slots into the amorphous core.
Notwithstanding significant study surrounding the use of amorphous metals in electric machines, to date it has proven very difficult to cost effectively provide a readily manufacturable electric device, which takes advantage of low loss materials, and many have abandoned attempts to develop a commercially viable electric machine having a magnetic core of amorphous metal. Thus it would be desirable to provide a highly efficient electric device, which takes full advantage of the specific characteristics associated with low loss material, thus eliminating the disadvantages associated with the prior art. Preferably, the low-loss material is an amorphous metal, a nanocrystalline metal, an optimized Si—Fe alloy, a grain-oriented Fe-based material or a non-grain-oriented Fe-based material.